GWT charts without JSNI, plugins, or server round-trips

The main idea behind GChart is simple: You can make very nice charts efficiently out of a reasonably small number of 1-cell Grids (for the aligned labels) and (empty) Images (for everything else), styled and positioned appropriately on an AbsolutePanel. Not surprisingly, bar charts don't suffer at all under the limitations imposed by this strategy--but (as long as you don't mind using dotted connecting lines or banded-filled pie slices) line and pie charts also do remarkably well 

Hung, Deadlocked, or Looping Process

• Print thread stack for all Java threads:
  • Control-\
  • kill -QUIT pid
  • jstack pid (or jstack -F pid if jstack pid does not respond)
• Detect deadlocks:
  • Request deadlock detection: JConsole tool, Threads tab
  • Print information on deadlocked threads: Control-\
  • Print list of concurrent locks owned by each thread: -XX:+PrintConcurrentLocks set, then Control-\
  • Print lock information for a process: jstack -l pid
• Get a heap histogram for a process:
  • Start Java process with -XX:+PrintClassHistogram, then Control-\
  • jmap -histo pid (with -F option if pid does not respond)
• Dump Java heap for a process in binary format to file:
  • jmap -dump:format=b,file=filename pid (with -F option if pid does not respond)
• Print shared object mappings for a process:
  • jmap pid
• Print heap summary for a process:
  • Control-\
  • jmap -heap pid
• Print finalization information for a process:
  • jmap -finalizerinfo pid
• Attach the command-line debugger to a process:
  • jdb -connect sun.jvm.hotspot.jdi.SAPIDAttachingConnector:pid=pid
    

Post-mortem Diagnostics, Memory Leaks

• Examine the fatal error log file. Default file name is hs_err_pidpid.log in the working-directory.
• Create a heap dump:
  • Start the application with HPROF enabled: java -agentlib:hprof=file=file,format=b application; then Control-\
  • Start the application with HPROF enabled: java -agentlib:hprof=heap=dump application
  • JConsole tool, MBeans tab
  • Start VM with -XX:+HeapDumpOnOutOfMemoryError; if OutOfMemoryError is thrown, VM generates a heap dump.
• Browse Java heap dump:
  • jhat heap-dump-file
• Dump Java heap from core file in binary format to a file:
  • jmap -dump:format=b,file=filename corefile
• Get a heap histogram for a process:
  • Start Java process with -XX:+PrintClassHistogram, then Control-\
  • jmap -histo pid (with -F option if pid does not respond)
• Get a heap histogram from a core file:
  • jmap -histo corefile
• Print shared object mappings from a core file:
  • jmap corefile
• Print heap summary from a core file:
  • jmap -heap corefile
• Print finalization information from a core file:
  • jmap -finalizerinfo corefile
• Print Java configuration information from a core file:
  • jinfo corefile
• Print thread trace from a core file:
  • jstack corefile
• Print lock information from a core file:
  • jstack -l corefile
• Attach the command-line debugger to a core file on the same machine:
  • jdb -connect sun.jvm.hotspot.jdi.SACoreAttachingConnector:javaExecutable=path,core=corefile
• Attach the command-line debugger to a core file on a different machine:
  • On the machine with the core file: jsadebugd path corefile
    and on the machine with the debugger: jdb -connect sun.jvm.hotspot.jdi.SADebugServerAttachingConnector:debugServerName=machine
• libumem can be used to debug memory leaks.

Writing web apps today is a tedious and error-prone process. Developers can spend 90% of their time working around browser quirks. In addition, building, reusing, and maintaining large JavaScript code bases and AJAX components can be difficult and fragile. Google Web Toolkit (GWT) eases this burden by allowing developers to quickly build and maintain complex yet highly performant JavaScript front-end applications in the Java programming language.

With Google Web Toolkit (GWT), you write your AJAX front-end in the Java programming language which GWT then cross-compiles into optimized JavaScript that automatically works across all major browsers. During development, you can iterate quickly in the same "edit - refresh - view" cycle you're accustomed to with JavaScript, with the added benefit of being able to debug and step through your Java code line by line. When you're ready to deploy, GWT compiles your Java source code into optimized, standalone JavaScript files. Easily build one widget for an existing web page or an entire application using Google Web Toolkit.